Disney is great if you've never been before if your an adult. Otherwise it's only the rides that really keep me going back. It depends what you are looking for the rides that have already been mentioned are the best but the likes of splash mountain and big thunder mountain in the magic kingdom can't be missed. And then of course there is just the 'magic' of disney, I always get a buzz when i go there, sad i know but it happens
If terrifying rides are what your looking for and you have a day free try Universal Islands of adventure, they will far surpass disney for simple hair raising factor. However this park along with Universal studios can take a couple of days on it's own so perhaps better to leave it and do disney properly this time!
Hope you have a good time!